As the field of orthopedics has advanced, increasing types of constructs have been developed for implantation into human and other animal bodies. There is heightened sophistication in the interplay between the implant, the bone, or bones, the surrounding soft tissue, and the fastener. For example, as the field has developed an understanding has also developed that an implant, such as a plate, can be used to support bone fragments in close, or even compressed association in order to promote the fusion of the fragments, or segments. This has lead to plates, which have a structure that is increasingly designed to function in the healing process, rather than merely acting as a scaffold. For example, an orthopedic surgeon can use an orthopedic implant to reduce a fracture or to rebuild a shattered bone, as well to hold segments of a joint in compression to allow for fusion. Thus, the implant is designed with the understanding that the biological environment is not ever exactly static, and the forces that are applied by the implant to the bone, and by the bone and soft tissue back to the implant will influence the healing or even the restructuring of a bone or bones. Moreover, these plates are increasingly structured to have an anatomical contouring rather than a flat planar shape.
An essential aspect of the proper functioning of the construct is the fastening means that forms the attachment between the implant and the bone. These fastening means can include various types of screws, threaded and non-threaded pegs, k-wires, hooks and other anchoring means. The implants typically include plates, rods, spacers, and cages and implants can include multiple fasteners. Further, the fasteners have various types of interfaces with the implant, including a multiaxial relationship, or a locking relationship or a locking variable axial relationship. In the instance in which the fastener has a ball and socket interface with the implant, the angle at which the fastener is held in the bone is less critical since the implant can receive the fastener at a variety of angles. However, in some instances, it is desirable that the plate be held to the plate at a defined angle. In the prior art, plate surfaces might be planar, and the fastener simply resided in the bone more or less perpendicular to the plate. However, much more sophisticated plate design may dictate fastener holes in the plate that are at a desired angle in a non-planar plate. In this instance, the plate surface is no longer a satisfactory reference for determining the angle to drill in the bone for receiving the fastener.
Constructs are often designed so that the fasteners will reside in the bone and locked relative to the plate at a desired angle so that the construct achieves the optimal stability, the optimal pull-out values for the fasteners, and or the optimal fixation for typical fragments. There are present designs in distal radius plates, as an example, typically where pegs are located and angled to capture various types of fragments that result from the most common breaks. These plates might have a head design with 4 or 7 holes at designated angles so that a surgeon has the option of choosing one, two, all, or some number in between, in order to best set a broken radial fracture.
Often the surgical procedure includes a step of drilling holes in the bone or bones in order to accommodate fastening devices such as screws or pegs used to anchor implants within a patient's body. For instance, screws have been used to anchor plate systems to the long bones of patients for stabilizing a variety of fractures or correcting disorders.
One commonly used technique for inserting a fastening screw into the bone includes the preparation of a pilot hole through the cortical surface of the bone and into the cancellous portion before inserting the screw therein. Typically, the selection of the insertion point is made based on the desired placement of the plate on the bone in relation to the break. Once the insertion point has been selected, a drill guide may be used separately or in conjunction with the plate to guide the drill bit along a desired axis, and/or to set the depth to which the drill bit penetrates the bone. These guides typically have a distal end, which may screw into an internal thread if the plate hole is threaded. Alternatively, the guides may include a tapered end, which can be jammed into the hole. While the former style of guide has the advantage of setting the angle for the screw relative to the plate, it can be cumbersome, time consuming and often difficult to screw the drill guide into these holes. While the taper fit has the advantage of a relatively easy interface, it does not guarantee the angle of the axis of the screw, in the bone or relative to the plate. One prior art guide include an overlay that is fixed to a distal radius plate to fix the angles of multiple holes for various screws or pegs used to fix the head to the distal portion of the radius bone.
The present invention relates to a surgical drill guide having a drill guide body which receives and guides a drill bit and which has a distal end for placement through a mating opening in a bone implant so that the distal end is substantially adjacent an exterior surface of a bone which is intended to receive a bone fastener. The implant is specifically a plate. The drill guide can be used with locking or non-locking fasteners, but is advantageously used with locking fasteners in which the angle of the fastener relative to the axis of the fastener hole is critical to proper functioning of the construct. Thus, the invention relates most specifically to a drill guide system comprising a drill guide used in conjunction with a plate having a threaded hole which receives the threaded head of a bone fastener. The distal end of the drill guide includes an interface which mates with the plate so as to position the drill guide for placement and axial alignment of a hole in the bone that receives a fastener for the implant. The body of the drill guide is held in place relative to the implant so as to define the angle as well as the location of the fastener hole in the bone.
The drill guide of the present invention that has the ease and simplicity of use of a single hole drill guide. This allows the surgeon the best visual access to the bone, but as it has an interface that forms a removable key fit with the plate so that the guide that can be easily inserted and locked from rotation, as well as into a specified angle relative to the screw hole. By “key fit” it is meant that there is a relationship which is a sliding relationship in the longitudinal direction and in a radial direction about that longitudinal axis, there is a radial locking relationship such is formed between a channel having a complex or non circular cross-section. After the pilot hole has been drilled, the drill guide is easily and quickly removed from engagement with the key hole in the plate and moved to a further hole in the plate.
The key fit preferably includes the mating interface between the longitudinal surface of the drill guide tip and recesses (which interrupt the thread) in or around the fastener hole in the plate, which can be a keyway and key that is formed by projections that are respectively hemi-cylindrical, or more ridge-like contiguous (meaning proximal to or adjacent in space) radial (meaning extending radially when viewed in a cross section) projections along the long axis of the drill guide tip that mate with corresponding female shaped recesses in or around the fastener hole. There can be two or more projections, with two to six, and preferably three or four, being ideal. Fewer projection decrease the possibility of stripping the projections and increase the security of the locking, while more projections make it easier to find the proper orientation of the drill guide tip in the recess. Also, the drill guide may include a flat shoulder that seats on a flat internal surface of the fastener recess. Thus, the fastener hole may include a counterbore defining a rim that captures a shoulder on the drill guide tip. The drill guide may also include a means to determine the drill depth, such as a marked fenestration along the shaft of the drill guide body.